Four valve cylinder head for a four cycle engine

ABSTRACT

An air-cooled single cross-flow cylinder head for motorcycle internal-combustion engines having a camshaft for valves controlling charge cycle ducts and with a scavenging direction S R  aligned with the course of charge cycle ducts in the cross-flow cylinder head. The engine is provided with a relatively stiff valve drive with inlet and outlet valves and ducts arranged in planes which are essentially in parallel with respect to the scavenging direction and where the camshaft operates the valves by tappets arranged in driving connection with rocker arms in the cross-flow cylinder head.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an air-cooled single cross flow cylinder headmotorcycle internal-combustion engines having a crankshaft pointing inthe driving direction of the motorcycle

ft. This camshaft controls overhead inlet and outlet

through rocker arms. The engine has a scavenging direction which isapproximately aligned with respect to charge cycle devices in thecylinder head and encloses an acute angle α, with the axis of rotationof the camshaft

An internal-combustion engine of this general construction is known inDE-A-No. 27 03 520. The engine therein is a flat twin engine havingcross-flow cylinder heads and a camshaft arranged in each cylinder headin parallel to the crankshaft and pointing into the driving direction.Each cylinder-head comprises one inlet and outlet valve which arearranged in a plane which is in parallel to the crankshaft and risestoward the outside. The camshaft, which is in parallel to the respectivevalve plane, acts upon the valves through rocker arms. The inlet andoutlet duct of each cylinder head is arranged relative to the respectivevalve plane in such a manner that a scavenging direction exists whichfalls from the rear top of the engine toward the front bottom and whichencloses an acute angle with the axis of rotation of the camshaft.

The above-described arrangement requires a timing case which isessentially placed on the cylinder head and disadvantageously enlargesthe overall dimensions of the flat twin engine and also results in acenter of gravity of the internal-combustion engine which is locatedhigher above the road surface.

Furthermore, a V-2 engine having cross-flow cylinder heads is known fromVolume 31b of the Third Edition of "Mitteilungen des Institutes forVerbrennungskraftmaschinen und Thermodynamik" (Information of theInstitute for Internal-Combustion Engines and Thermodynamics) of theTechnical University of Graz from Illustrations 9.4T 2f-2g/II. Thevalves of this engine are arranged in planes which are essentially inparallel to the respective scavenging direction. However, here all thevalves are actuated by a single camshaft, arranged between the cylindersin the engine power section, in parallel to the crankshaft. Thisrequires a expensively constructed transmission. Here valve levers areactuated by the camshaft through relatively long push rods and rockerarms arranged in the cylinder heads for the control of the valves.Because of the relatively high oscillating masses and a high elasticityin the transmission, a precise valve control is hardly possible withacceptable expenditures. This results, in addition to unfavorable fuelconsumption and exhaust values construction, in a machine with a reducedperformance and rotational speed. Furthermore in this arrangement,considerable mechanical noise is created for an air-cooled engine andthis also require relatively short servicing intervals for the valvesdue to the valve play changes.

It is the object of the invention to provide an internal-combustionengine of the above-mentioned construction, without the above-mentioneddisadvantages. The invention allows for a relatively stiff valve controlin a small installation space. Here several identical valves arearranged in an area of the cross-flow cylinder heads which iswell-cooled by the air stream. This object is achieved by having inletand outlet valves arranged in planes which are essentially in parallelwith respect to the scavenging direction of the engine and with thevalve camshaft in driving connection with the rocket arms through hollowtappets arranged in the cross-flow cylinder head.

An advantage of the invention is that the valve camshaft can be arrangedat a minimum distance and next to the valve arrangement. It usestransmission elements of a small or short construction. Thus a stiffvalve drive is achieved while, on the whole, the installation space issmall and the arrangement is compact.

Here where the internal-combustion engine is constructed as a flat twinengine with cylinder heads which are cooled by an air stream, severaloutlet valves for each cylinder head may be advantageously arranged inareas which are cooled by the directly approaching air stream. Otherdeveloping possibilities of the valve arrangement are not significantlylimited by the invention. For this reason, in a further development, across-flow cylinder head is therefore preferred which has four valveswhich are arranged overhead in a V-position. Here, a relatively smallV-angle is preferred between the groups of identical valves forachieving a flat roof combustion chamber in the cylinder head. Inaddition, a centrally arranged spark plug may be provided in parallel tothe cylinder axis.

In order to achieve a simple construction of a cross-flow cylinder head,a separate bearing bracket is provided as the support for the valvecamshaft as well as for housing hollow tappets interacting with theshaft, so as to provide a driving connection with rocker arms which arealso arranged at the bearing bracket. This bearing bracket, which isconstructed as a single mounting unit, is held by means of a screwedconnection with the cylinder head, the tension rods of which may also befixed in the engine power section.

In order to reduce the overall height of the cross-flow cylinder head, achamber is provided in the head, which is open on the cylinder-headcover side, for receiving the camshaft arranged overhead at the bearingbracket. A relatively narrow chamber is sufficient for the camshaftwhich is arranged at the bearing bracket in divided bearings. Furtherthe valve camshaft may have a short construction. The short constructionis promoted by an additional design of the cross-flow cylinder head, sothat a driving device of the camshaft may also be housed in the chamber.Finally, it is advantageous to arrange the chamber in the area of thecylinder head which is predominantly on the engine inlet side, becausestress to the enclosed valve gear caused by temperature will be reducedby the relatively cool area of the cylinder head.

The bearing bracket, which requires little installation space, for theabove-described preferred 4-valve arrangement, has guides for the hollowtappets which are arranged between the parallel shafts of the rockerarms. As a result, the rocker arms have short and therefore stiff arms.These rocker arms have sliding surfaces which are constructed ascylinder surfaces to provide a perfect, low-wear and slidably movableconnection with flat or slightly spherical faces of the straight hollowtappets.

Finally, within the scope of the invention, a bearing bracket isprovided for a rocker shaft which is approximately in parallel to thescavenging direction and which can drive a 2-valve or 3-valve cross-flowcylinder head.

In a flat twin engine having a crankshaft pointing in the drivingdirection and having camshafts which are parallel to this crankshaft,the invention provides a scavenging direction which slopes down indriving direction with a preferred multiple outlet valve arrangement.The required pipe length for an exhaust system can be achieved byenclosing the cylinder partially in an actuated manner. The scavengingdirections of both cylinder heads may, in addition, extend in planeswhich are essentially in parallel with respect to the longitudinal axisof the vehicle, or of the engine. Alternatively the planes can be slopedwith respect to one another against the driving direction. As a result,the intake pipes which, according to the scavenging direction can extendin driving direction from the upward rear part of the engine toward thebottom front, may be placed advantageously with respect to sufficientleg room at the motorcycle by means of a spatially acute-angledarrangement of the scavenging device with respect to the camshaft

For the construction of the valve control, the common arrangement of thevalve gear and the transmission elements (rocker arms and tappets) in acommon bearing bracket is also advantageous. This bearing bracketresults in a stiff, complete and space-saving OHV valve control. Thispermits small valve angles and a central spark plug position for anoptimal combustion chamber. This has a favorable effect on theinternal-combustion engine with respect to its performance, torque,elasticity, and to its noise, fuel consumption and exhaust quantity.Finally, the bearing bracket results in advantages during seriesassembling and simplifies the cross-flow cylinder head with respect tocasting and manufacturing techniques.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lateral view of a flat twin engine showing a top view of across-flow cylinder head;

FIG. 2 is a sectional view according to Line II--II of the cylinder headwith a bearing bracket placed on it for the valve control;

FIG. 3 is another embodiment of a bearing bracket

DETAILED DESCRIPTION OF THE DRAWINGS

A flat twin engine 2, equipped with two cylinders 1, is arranged in avehicle, (not shown) with its crankshaft 3 being aligned in a drivingdirection F_(R). Each cylinder 1 is equipped with a cylinder head 4constructed according to the cross-flow principle. A camshaft 6 isarranged in the cross-flow cylinder head 4, in parallel with respect tothe crankshaft 3, and is driven by means of an enveloping gear 5, Aninlet duct 7 on one side of the cylinder head and an outlet duct 8 onthe opposite side of the cylinder head determine the flow-through orscavenging direction (arrow S_(R)) of the cross-flow cylinder head 4. Asshown in FIG. 1, the cross-flow cylinder head 4 (viewed in top view) hasa scavenging direction S_(R) which extends at an acute angle ofapproximately 8° to 20° with respect to the axis of rotation 9 of thecamshaft 6. The scavenging direction S_(R) is directed downward towardthe front with respect to the driving direction F_(R). A pair of outletvalves 10 are arranged in the cylinder head 4, in front with respect todriving direction F_(R), and a pair of inlet valves 11 are arranged inthe rear.

The respective two outlet valves 10 and inlet valve 11 are arrangedoverhead in a V-position, at a relatively small V-angle in the cylinderhead 4, in planes E₁ which are essentially parallel to the scavengingdirection S_(R). This Provides for of an optimal roof-shaped combustionchamber for the cylinder head 4 (not shown). This cylinder head 4, has areceiving space 12 for a spark plug (not shown) in the area of thecombustion chamber center between the inlet valves 11 and the outletvalves 10.

A bearing bracket 13, which is separate from the cross-flow cylinderhead 4, has a bridge 14 aligned with the camshaft 6 and contains guides15 for short hollow tappets 16. As shown in FIG. 2, the bottoms of thehollow tappets 16 interact with cams 33, 34 on the camshaft 6 and aresupported by bearings 17 attached to the bridge 14. At the top, thehollow tappets 16 interact with rocker arms 18 and 19, which arearranged in the bearing bracket 13 so that they can be tilted aroundsupport shafts 20 which are spaced away from one another in parallel andare arranged transversely to the scavenging direction S_(R). The outletvalves 10 are actuated by a common rocker 18 and the inlet valves 11 areactuated by a common rocker 19. The rocker arms 18 and 19 are driven byhollow tappets 16 by means of short arms 21 and 22 which arranged in thebridge 14 of the bearing block 13 between the two rocker shafts 20. Onthe top rocker side, the hollow tappets 16 have flat or slightlyspherical faces 23. The rocker arms 21 and 22 have cylinder surfaces 24which provide slidingly movable connection with the spherical faces 23of the tappets 16. The axes of the cylinder surfaces 24 extend inparallel to the axis of the rocker shafts 20.

The bearing bracket 13 forms, a mounting unit with the camshaft 6, thehollow tappets 16 and the rocker arms 18 and 19. This mounting unit canbe moved around the shafts 20 and is held at the cross-flow cylinderhead 4 by a screwed connection 25 with the cylinder head 4.

As shown in FIG. 2, the camshaft 6 is arranged in divided bearings 17 atthe bridge 14 of the bearing bracket 13. As a result, relatively largediameters are avoided for the camshaft 6, which is disposed overhead atthe bearing bracket 13, or at its bridge 14. In order to keep theoverall height of the cross-flow cylinder head 4 low, the cross-flowcylinder head 4 has a chamber 26 which accommodates the camshaft 6 and asignificant part of the bridge 14 of the bearing bracket 13. The chamber26 is arranged in the cylinder head 4, essentially behind the centerplane E_(ZM) of the cylinder and between an outer road surface sidecontour 27 of the cylinder head and the inlet valve 11 which is locatedclosest to this contour. In its longitudinal dimension, the chamber 26is essentially delimited by a cylinder head boundary 28 on the inletside and a charge cycle duct 29 on the outlet side. In the end area ofthe cross-flow cylinder head 4 on the inlet side, the chamber 26 isconnected with a breakthrough 31 arranged in the cylinder head bottom30. This breakthrough 31 is penetrated by a drive chain 35 for theenveloping gear 5 which is used for driving the camshaft 6. As a resultof an intermediate drive (not shown) and which is geared down 2:1, theenveloping gear 5 on the camshaft 6 may have a chain wheel 32 with arelatively small diameter. As a result of the arrangement of theenveloping gear 5 for the drive of the camshaft 6 in the relatively coolinlet area of the cross-flow cylinder head 4, it is also possible toextend the camshaft 6 beyond the cylinder head boundary 28 for anexterior enveloping gear with a toothed belt.

FIG. 2 shows that the camshaft 6, with its two spaced cams 33 and 34ends and with the overhung cam 34 close to the outlet charge cycle duct29. By having the bearing arrangement for the camshaft 6 at the bearingbracket 13 toward the rear of each cam 33, 34, the longitudinaldimension of the chamber 26 is kept small. In addition, a relativelylarge clearance is obtained for the camshaft 6 with an axis of rotation9 of the camshaft 6 which extends at a spatially acute angle withrespect to the scavenging direction S_(R).

Within the framework of the invention according to FIG. 3, a bearingbracket 36 has a rocker shaft 37 for rocker arms 38 and 39 which isdirected transversely to the cylinder center plane E'_(ZM), foractuating of an inlet valve 11' and an outlet valve 10'. In thisembodiment, the rocker axis 37 for a 2-valve cross-flow cylinder head 4'points approximately in the direction of the scavenging direction S_(R).

Although the present invention has been described and illustrated indetail, it is to be clearly understood that the same is by way ofillustration and example only, and is not to be taken by way oflimitation. The spirit and scope of the present invention are to belimited only by the terms of the appended claims.

What is claimed:
 1. A motorcycle internal-combustion engine having across-flow air-cooled single cylinder head, comprising:a crankshaft withan axis pointing in a driving direction of the motorcycle; a camshaft inthe cross-flow cylinder head, having its rotation axis arrangedessentially in parallel to the crankshaft; the camshaft controlsoverhead inlet and outlet valves for engine charge cycle ducts by rockerarms; the cross-flow cylinder head has a scavenging direction at anacute angle (α) with the axis of rotation of the camshaft; the inlet andoutlet valves are arranged in planes, each of said planers including arespective inlet and outlet valve, said planes being essentially inparallel with respect to the scavenging direction; and wherein thecamshaft is in driving connection with the rocker arms by tappetsarranged in the cross-flow cylinder head.
 2. An internal-combustionengine according to claim 1, whereinthe scavenging direction is, as seenin top view of the cross-flow cylinder head, in a motorcycle drivingdirection and is sloped down toward the front of the motorcycle at anangle (α) of between 8° and 20°.
 3. An internal-combustion engineaccording to claim 2, whereinthe cross-flow cylinder head comprisesoverhead inlet and outlet valves arranged in a relatively small V-angle,wherein the outlet valves are arranged toward the front drivingdirection and the inlet valves arranged in the rear.
 4. Aninternal-combustion engine according to claim 3, whereinthe cross-flowcylinder head is equipped with a separate bearing bracket means forsupporting the rocker arms and the tappets; wherein the bearing bracketmeans has a bridge aligned with the camshaft and has guide means for thetappets which are configured as short cylindrical hollow tappets, andwhich interact between the rocker arms and cams on the camshaft; andwherein the camshaft is arranged in bearing support at the bridge.
 5. Aninternal-combustion engine according to claim 4, whereinthe camshaft issupported by divided bearings by the bridge of the bearing bracket;wherein the bearing bracket means forms a mounting unit containing thecamshaft, the hollow tappets and the rocker arms; and wherein the rockerarms are movably mounted on support shafts arranged on the mountingunit.
 6. An internal-combustion engine according to claim 5, whereinthecross-flow cylinder head has a chamber located in a rear side of thecylinder head between an outer contour and an adjacent inlet valve, at arear end of the engine, and which extends forwardly from a cylinder headboundary at the inlet side to an outlet charge cycle duct at the frontend of the engine, and wherein the chamber encloses the camshaft whichhas the cams spaced away from one another by the bearing supported bythe bridge of the bearing bracket, and wherein one of the cams islocated adjacent to the outlet duct side as an overhung cam.
 7. Aninternal-combustion engine according to claim 6, whereinthe chamber isconnected to a breakthrough arranged in the cylinder head bottom at aninlet-side end area of the cross-flow cylinder head, and wherein thisbreakthrough is penetrated by a driving device on the camshaft.
 8. Aninternal-combustion engine according claim 1, wherein the inlet andoutlet valves are arranged in a V-shape in the cross-flow cylinderhead;wherein a spark plug is arranged in an area of a cylinder centerplane directed transversely with respect to the scavenging direction;wherein a bearing bracket supports two rocker arm shafts arranged inparallel on both sides of the cylinder center plane; wherein each rockerarm actuates several identical valves; and wherein the tappets arearranged in a bridge of the bearing bracket between the two rockershafts.
 9. An internal-combustion engine according claim 2, wherein theinlet and outlet valves are arranged in a V-shape in the cross-flowcylinder head;wherein a spark plug is arranged in an area of a cylindercenter plane directed transversely with respect to the scavengingdirection; wherein a bearing bracket supports two rocker arm shaftsarranged in parallel on both sides of the cylinder center plane; whereineach rocker arm actuates several identical valves; and wherein thetappets are arranged in a bridge of the bearing bracket between the tworocker shafts.
 10. An internal-combustion engine according claim 3,wherein the inlet and outlet valves are arranged in a V-shape in thecross-flow cylinder head;wherein a spark plug is arranged in an area ofa cylinder center plane directed transversely with respect to thescavenging direction; wherein a bearing bracket supports two rocker armshafts arranged in parallel on both sides of the cylinder center plane;wherein each rocker arm actuates several identical valves; and whereinthe tappets are arranged in a bridge of the bearing bracket between thetwo rocker shafts.
 11. An internal-combustion engine according claim 4,wherein the inlet and outlet valves are arranged in a V-shape in thecross-flow cylinder head;wherein a spark plug is arranged in an area ofa cylinder center plane directed transversely with respect to thescavenging direction; wherein the bearing bracket supports two rockerarm shafts arranged in parallel on both sides of the cylinder centerplane; wherein each rocker arm actuates several identical valves; andwherein the tappets are arranged in the bridge of the bearing bracketbetween the two rocker shafts
 12. An internal-combustion engineaccording to claim 8, wherein the tappets act upon cylinder surfaces onthe rocker arms through slightly spherical faces; andwherein the axes ofthe cylinder surfaces are in parallel to the rocker shafts.
 13. Aninternal-combustion engine according to claim 9, wherein the tappets actupon cylinder surfaces on the rocker arms through slightly sphericalfaces; andwherein the axes of the cylinder surfaces are in parallel tothe rocker shafts
 14. An internal-combustion engine according to claim10, wherein the tappets act upon cylinder surfaces on the rocker armsthrough slightly spherical faces; andwherein the axes of the cylindersurfaces are in parallel to the rocker shafts.
 15. Aninternal-combustion engine according to claim 11, wherein the tappetsact upon cylinder surfaces on the rocker arms through slightly sphericalfaces; andwherein the axes of the cylinder surfaces are in Parallel tothe rocker shafts.
 16. An internal-combustion engine according to claim1, wherein the bearing bracket is held to the cylinder head by a screwedconnection.
 17. An internal-combustion engine according to claim 2,wherein the bearing bracket is held to the cylinder head by a screwedconnection.
 18. An internal-combustion engine according to claim 1,wherein the bearing bracket has a single rocker shaft for both the inletvalve and the outlet valve and wherein said rocker arm shaft is directedtransversely with respect to the cylinder center plane.
 19. Aninternal-combustion engine according to claim 2, wherein the bearingbracket has a single rocker shaft for both the inlet valve and theoutlet valve and wherein said rocker arm shaft is directed transverselywith respect to the cylinder center plane.
 20. An internal-combustionengine according to claim 3, wherein the bearing bracket has a singlerocker shaft for both the inlet valve and the outlet valve and whereinsaid rocker arm shaft is directed transversely with respect to thecylinder center plane.